TheDirty wrote:Not certain how that would be useful, since it would be airspeed measured and relative to ambient wind, not actual speed across the water.
If you want faster, there are plenty of straight analog absolute pressure sensors on Digikey, Mouser, or any major distributor. Hook it up to an ADC and measure the pressure yourself.
EDIT: Ah, I see, the way it is setup it measures the difference from total and static pressure. It also says, it's not all the accurate below supersonic speeds? That's quite a calculation with temp and ambient pressure, though. Seems like it would be fairly difficult to get really accurate.
It should be quite accurate assuming there is not a high wind blowing directly in either of the ports, this is the tradeoff. This method should be much more accurate than GPS velocity. There are other alternatives such as a Doppler Velocity Log (DVL) instrument to measure boat speed ($30k+) if you need mm/s accuracy.
Again, you cannot use a single pressure sensor to accurately measure velocity. The nasa site says "If the velocity is very high (supersonic), we've violated the assumptions of Bernoulli's equation and the measurement is wrong", so it is not accurate ABOVE supersonic speeds.
Pitot tubes can be very accurate when properly calibrated, that's why they are used in most fluid flow measurement systems, including wind tunnels, and every airplane (You will see multiple pitot tubes, sometimes temp controlled, on the front of every commercial airplane)